1. Field of the Invention
The present invention relates to a process for preparing urethanes and carbonates and, more particularly, relates to a new and useful process for preparing urethanes from amines, carbon dioxide and an allyl halide and for preparing carbonates from alcohols, carbon dioxide and an allyl halide.
2. Prior Art
Urethanes and carbonates have been typically synthesized by the reaction of a primary amine or an alcohol with phosgene to form an isocyanate or carbonate. Thereafter, the isocyanate is reacted with an alcohol to form the corresponding urethane. Phosgene is very toxic and thus requires very careful handling from a product and worker safety standpoint. Isocyanates are sensitizers and are extremely toxic as well. Preparing urethane products without using phosgene in an economical manner and without generating isocyanates would be an achievement of considerable significance in the art.
U.S. Pat. No. 4,467,089 discloses the preparation of certain carbamic acid derivatives by the simultaneous reaction of a secondary amine and a tertiary amine with carbon dioxide to produce corresponding tertiary amine salts of N-substituted carbamic acid. The secondary and tertiary amines are brought together in equimolar proportions in the presence of excess carbon dioxide under mild conditions. The secondary amine reacts with CO.sub.2 in the presence of the tertiary amine to form the corresponding disubstituted tertiary ammonium carbamate salt. The salt is described as being useful as heat activatable delayed action catalysts, especially for use in polyurethane formulations.
In Chemistry Express, Vol. 1, No. 4, pp 224-227 (1986), Kinki Chemical Society, Japan, it is disclosed that primary and secondary amines absorb CO.sub.2 to form carbamic acid amine salts and that when an equivalent of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is added, additional CO.sub.2 is absorbed to form the DBU-carbamate salt. The DBU-carbamate salt when reacted with an alkylating agent forms a carbamate ester (urethane). Yield and selectivity of the urethane product are highly dependent on the nature of the alkylating agent. When dibutylamine is reacted with CO.sub.2 in the presence of DBU and the resulting DBU-carbamate salt is reacted with butyl chloride as the alkylating agent, a yield of only 7% is realized. With butyl bromide, the yield is 86%.